The invention relates to an add-on shaft for an electric motor and method for connecting an add-on shaft to the drive shaft of an electric motor. In particular, the invention relates to an add-on shaft for driving a rotary encoder or impeller fan.
As is generally known, an electric motor converts electrical energy into mechanical energy. Most electric motors have a rotary shaft for this purpose. Machines, subassemblies or other devices driven by the electric motor can be coupled directly or indirectly to the motor's shaft.
Various embodiments of electric motors are well known—often referred to simply as motors, below. In particular, these embodiments include self-ventilated motors and force-ventilated motors and also motors fitted with a brake.
The rotational speed or position sensing provided by a rotary encoder can be used to control rotational speed and/or position, and combining a rotary encoder with an electric motor for that purpose is already known. The rotary encoder is coupled to the motor shaft and respective embodiments of the motor require motor shafts of different lengths. Coupling a fan impeller and/or a brake, for example, or coupling the rotary encoder, in any case, requires extending beyond the rotor/stator area of the motor, to enable them to be connected to the motor.
To avoid constructing different types of motors having motor shafts of different lengths, it is already known to extend it by using an add-on shaft on the side of the motor where the rotary encoder will be coupled to the motor. The add-on shaft is axially affixed to the motor shaft by introducing a pin provided for this purpose into a centered, blind hole drilled in the motor shaft and fixing that pin there, particularly by using an adhesive.
Hitherto, a problem with add-on shafts and also with their connection to the motor shaft, has been a less than optimum stability of the connection with the motor shaft in some instances, and the concentric position of the add-on shaft relative to motor shaft being sometimes less than fully satisfactory.